1. Field of the Invention
The present invention relates to an image forming apparatus that forms a latent image on an image bearing member by using, for example, an electrophotographic system or an electrostatic recording system, and that develops the latent image to form a visual image.
2. Description of the Related Art
Known electrophotographic image forming apparatuses sometimes use a developing unit having a developing roller serving as a toner bearing member that develops an electrostatic latent image and a supply roller serving as a toner supply member that rotates with the developing roller in contact therewith to thereby supply toner to the developing roller. The supply roller generally has a urethane sponge layer, which is a foamed layer, on the surface thereof to hold the toner to be supplied to the developing roller. An example of such a developing unit is disclosed in Japanese Patent Laid-Open No. 2009-009035. FIG. 7 shows the developing unit disclosed in Japanese Patent Laid-Open No. 2009-009035, in which a developing roller 1 and a supply roller 2 having a urethane sponge layer 2b is shown.
With the configuration using the toner supply member having a foamed layer, as described above, in the case where the developing unit is new, sufficient image density sometimes cannot be obtained because the foamed layer does not contain a sufficient amount of toner. Therefore, in the case where the developing unit is new, it is necessary to first rotate the toner supply member for a long time to soak the foamed layer with toner before image formation. Accordingly, in the case where a new developing unit is used, it sometimes takes much time to bring it into an image formable state.